The present invention relates to a method of embedding copyright management information in AV content that is distributed in a downloadable file format. More particularly, the present invention relates to MPEG-4 Intellectual Property Management and Protection (IPMP) for MPEG-4 media streams distributed in the MP4 file format.
There are two basic methods of distributing AV content, in streams or as downloadable files. In the stream distribution method the content supplier transmits AV content data in a stream that is reproduced as it is received on the receiver (player) side. The distributed content can therefore be reproduced with only a short wait after transmission begins. In the downloadable file model, however, the content supplier transmits the AV content data as a file. The receiver (player) can therefore start playback only after all AV content data has been received, and playback cannot start until all of the AV content data has been transferred to the receiver.
The present invention relates to a downloadable file format, and is described herein using the MP4 file format by way of example as a downloadable file format.
The MP4 file format is defined as a part of the MPEG-4 System specification. More specifically, however, the MP4 file format is a specific use of the more general ISO Base Media File Format. The MP4 file format is a generic file format enabling easy local manipulation of media data, and maintains streaming protocol independence. Media data in the MP4 file format is stored in its most natural format and is thus not fragmented.
The MPEG-4 System specification also defines the IPMP Extension specification as the mechanism for protecting media streams in the MPEG-4 System context. It defines, for example, how to protect a protected MP4 file format that is protected by encryption. In the IPMP mechanism an IPMP descriptor is stored in the MP4 file in addition to the protected media stream to enable determining which stream is protected and how. More precisely, the IPMP descriptor is stored in an object descriptor which contains other MPEG-4 System information as well. FIG. 1 shows the general architecture of the MPEG-4 IPMP protection scheme.
An MPEG-4 System compatible terminal can read object descriptors from an MP4 file, and can parse the descriptor further to read any IPMP descriptors stored in the object descriptors. The IPMP descriptor provides content information relating to how the associated media streams are protected and which IPMP tool should be used for further processing. This prior art is disclosed in non-patent reference 1.
Because the MP4 file format enables easy local manipulation of media data, many specifications other than MPEG-4, such as ISMA and 3GPP, also use the MP4 file format as their own default file format. Furthermore, for practical purposes, these specifications have the same requirement as the MPEG-4 System to protect the media stream by, for example, encryption. However, due to the lack of full MPEG-4 System support, it is not possible for these specifications to use already defined IPMP solutions to directly protect their own media stream. Given an MP4 file which contains IPMP protected streams, receivers compatible only with these specifications cannot recognize either the Object Descriptor or IPMP Descriptor. Furthermore, because the conversion information is only stored in the IPMP descriptors, these receivers have no means of determining if a received media stream is unrestricted or is protected. An alternative mechanism is therefore needed to enable these terminals to handle MP4 files in a protected media stream.
Non-patent reference 1: ISO/IEC14496-1/FDAM3 (ISO/IEC JTC1/SC29/WG11 N5282)